I'd take the Skyliner. Just understand that there will be a period of waiting (30 minutes???) at AoA for the Skyliner to start operating. Once it opens, the line moves pretty quickly. Since you want to do Guardians during EE, you'll want to be at the front of the pack and be prepared to walk quickly to get to it. Based on what bloggers are posting lately, you should be able to walk straight to Guardians once you get through the entrance at the International Gateway. The line at Guardians will get long quickly, but again, once the ride starts operating it will move at a decent pace. But I still think even being near the front of the pack, it will eat up about an hour of time once it opens (assuming you are not the very first people in line).
Leaving EP on the Skyliner after fireworks can be a little intimidating. That line builds quickly, but like others have said, it moves constantly. They put 8 people in each cabin at that time of the night, so the line does move fairly fast...though after a long day in the parks, it won't feel that way. We've handled the end of night Skyliner 2 different ways. One time we watched the fireworks from somewhere over near China. When they were over, we took our time walking to the Skyliner -- stopped for a drink, looked through some shops, bathroom stop, etc. When we got to the Skyliner, the line was still through all the switchbacks and may 50 ft. out into the walkway. We sat on a bench and people watched for 10-15 minutes before getting in line (which was much shorter by that point). I don't have my notes with me right now, but I'm pretty sure we were on the Skyliner by 10:00. Another time we watched the fireworks from the little island between United Kingdom & France (I think this is occasionally closed for special events -- but not always). We made sure we had our bags in hand as the finale of the fireworks started. And as soon as the last blasts went off, we started walking towards the Skyliner. We didn't power walk, but we kept moving at a decent pace. We walked through most of the switchbacks and were just about at the loading station when we hit the end of the line. We had about a 5-7 minute wait before getting on the Skyliner though by that point, the end of the line was way down the boardwalk. I don't remember having a long wait at CBR either time -- maybe 5-7 minutes.
ETA: While we drive over 1,000 miles to get to Disney, we don't do any driving once we're there. The last thing we feel like doing after a long day in the park is to get in an oven (we travel in June) and try to fight all the traffic leaving the parks at closing time. We prefer to sit on an air conditioned bus and look at all the cars barely moving while our bus driver navigates the roads or fly above all the cars in the cool Skyliner cabins. Using Disney transportation works best for us, but YMMV.
